Telegraph system



July 2, 1940. H. NYQuls'r TELEGRAPH SYSTEM Filed Sept. 24, 1938 SUB.

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TIME 0 /NVENTOR H. NVQU/S 7' 5y.

' ATTORNEY Patented July 2, 1940 UNITED STATES PATENT GFFICE 1.Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application September 24, 1938,Serial No. 231,488

8 Claims.

This invention relates to telegraph systems and more particularly to a,means of improving the transmission over telegraph loop circuits byreducing the bias inherent in the operation of certain Well-known loopcircuits now widely used in the art.

In these Well-known loopcircuits, the current owing between thetelegraph relay armature and one of its associated contacts differswidely in value from the current flowing through said armature and itsopposing contact. The effect of this invention is to equalize saidcurrent for the two conditions. Since the design of contact protectionnetworks is ailected by the variations of said current, this problem issimplied by this invention. The bias of the receiving relay in said loopcircuits, further, is affected, as now employed in the art, by thepresent contact protection networks. As a result of this invention theeffect of the contact protection networks on said bias is eliminated. Itis possible, therefore, as a result of this invention to design contactprotection networks without regard to their effect upon bias.

An object of this invention is to reduce bias in a telegraph circuit.

A further object of this invention is to eliminate bias in a telegraphcircuit caused by relay travel time.

A further object of this invention is to facilitate the design oftelegraph relay contact protection networks.

A further object of this invention is to equalize the current flowingbetween the armature and the marking and spacing contacts of a telegraphrelay transmitting into a balanced subscribers telegraph loop circuit.

A feature of this invention is the connection of one terminal of aresistance to the apex of a balanced telegraph loop circuit, saidresistance being equal in value to the resistance of said loop, thesecond terminal of said resistance being connected to marking battery,with theloop being terminated in spacing battery of equal value butopposite polarity from said marking battery.

A further feature of this invention is that the amount of currentflowing in the subscribers loop during the armature travel time of therelay transmitting into the loop, both from its marking to spacing andspacing to marking contacts, is just slightly less than is necessary tobalance the biasing current or spring tension on the'subscribersreceiving relay, so that said relay does not release nor operate untilsaid travel is ended in each instance, but does operate and release ineach instance the instant the travel is ended, thus insuring signalsequal in length to the transmitted signals.

These and other features will be apparent from the description of theoperation of Athe invention 5 hereinafter following read with referenceto the Various associated figures:

Fig. 1 is a well-known telegraph subscribers loop circuit to which thebias correction feature of this invention has been added. This featureis incorporated in resistance |08 and its connection to the battery |02and the apex of relay |09;

Figs. 2 to 5 are current-time curves forthe subscribers loop per Fig. 1by means ofwhich the eiiectiveness of the invention herein will. bedemonstrated.

Referring now to Fig.y 1, a telegraph subscribers. line circuit widelyused in teletypewriter switching systems is shown. Resistances |0I, y|03 and I4 are used to protect batteries .I 00 and |02 fromshortcircuit. The magnitude of their resistance values is negligible ascompared with the loop resistance and their eiect may be disregarded.

Fig. 1 will rst be described as arranged generally at present,disregarding resistance |08 and its connections. The effect of thevusual condenser and resistance contact protection devices |05, |06, |01and ||5 will not at present be considered.

The armature of sending relay |04 is actuated, by the eiiect of acircuit (not shown) with which we are not concerned,.to enga-ge itsrightand left-hand contacts alternately. When said armature is inengagement with its right-hand contact, a circuit may be traced, fromthenegative terminal of battery |02, through resistance |03, and theright-,hand contact and armature of relay |04 to the apex of relay |09.The circuit continues from the apex of relay |09 over parallel paths`One path continues through the bottom or biasing winding of relay .|09and resistance I|3 to ground. The other path extends through the top orline winding of relay |09, through resistance ||0, the subscribersstation apparatus and resistance ||4, to positive battery |00. For thiscondition, it may be observed, that the batteries |02 and |00 are inseries-aiding relationship. Resistance ||0 simulates the totalresistance of the loop. The resistance from the apex of relay |09 aroundthe loop is balanced by the resistance from `the apex through the bottomwinding of relay 09 and resistance I3 to ground.

When the armature of relay |04 is in engagement with its left-handcontact a circuit may be ||0, the top winding of relay |09, the bottomwinding of relay |09 and resistance l I3 to ground.

'Ihe values of the electromotive forces of batteries |00 and |02 areequal. Their values relative to the various resistances are such thatwhen the armature of relay |04 is in engagement with its right-handcontact, 60 milliamperes flows around the loop. When said armature is inengagement with its left-hand Contact the current" in the loop is Zero.And when said armature is disengaged from its contacts, the currentiiowing around the loop is 15 milliamperes.

Refer now to Fig. 2. This shows the subscribers loop current for theabove-described condition. The verticaliordinate represents current inmilliamperes. The abscissa represents time.

While the armature` is'in engagement with its right-hand contact, 60milliamperes is flowing around the subscribers loop. This is representedby the left-hand, horizontal line marked 00 on the vertical ordinate.The armature leaves its right-hand contact at the beginning of thearmature travel time. This is indicated at a which lprojects to Zero onthe horizontal time axis. The instant the armature leaves its right-handcontact, the loop current drops to 15 milliamperes. This occurs withoutany change in time. This is indicated by the line a-c. During the traveltime of the armature from the right-hand to left-hand contact, the loopcurrent is maintained at 15 milliamperes. `Thisis indicated by the linec-d'. The instant that the armature engages with its left-hand contactthe current drops from 15 milliamperes to 0. lThis is indicated by lined-a The armature is in engagement with its left-hand contact for aninterval of time represented by the line e-f. Then the armatureseparates from `its left-hand contact. The current rises instantly againto 15 milliamperes represented by the line f-g. During the -travel timeof the armature from its left-hand to its right-hand contact, the loopcurrent remains at 15 amperes. This is indicated by the line gh. At theend of the travel time represented by h, when the armature engages againwith its right-hand contact, the loop current rises again instantly,during Zero change in time to the original 60 milliamperes. This isrepresented by the line h-z'.

Let us now consider the effect of this train of events on the receivingrelay in the subscribers station equipment It will be assumed, for thepresent, that there is no delay between the transmission of a signal byrelay |04 and its reception at the subscribers station due to theelectrical characteristics of the circuit. We Will assume, also, thatthe receiving relay at the sub- 'scribers station releases at 29.9milliamperes and operates at 30.1 milliamperes.

The instant that relay |04 releases at the central station, thereceiving relay in the subscribers station will release as the line a-bpasses through 29.9 milliamperes. .This is indicated by the point markedRelease on line a-'-c. The time line a-c, therefore, denes the beginningof the spacing interval for both relays. For relay |04, the spacinginterval lasts during the travel period c-d and the time that itsarmature is in engagement with its left-hand contact e-f. The totalduration of the spacing interval is, therefore, measured by the time en-f. When the armature of relay |04 breaks from its lefthand contact, atthe end of its spacing interval, the loop current does not risesufliciently to operate relay which requires 30.1 milliamperes. It risesinstead only to 15 milliarnperes, where it remains until the end of thetravel time of relay |04 armature back to its right-hand contact, duringthe time measured by g-h. The receiving relay in does not operate to endits spacing interval until the loop current rises through 30.1 amperesas indicated in line h-i by the point marked Operate The spacinginterval for the receiving relay is, therefore, measured by the timea-i. It is greater than the spacing interval of the sending relay by thetravel time g-h. This is called in the art a spacing bias and it isinherent in circuits per Fig. 1 which are `widely used without thebenefit of this invention.

We will now consider the eiect of the connection of resistance |08between battery |02 and the apex of relay |09. Resistance |08 is equalin value to the total resistance from the apex of relay |00 around thesubscribers loop through battery |00 to ground. It is also equal,therefore, in value to the resistance from the apex of relay |09 toground through resistance H3. The t;

values of resistances |0|, |03 and ||4, which are used as an aid inprotecting batteries |00 and |02 against short circuit, are negligibleas compared with the value of resistance |08. When the armature of relay|04 is in engagement with contact |03, approximately 60 milliamperes owsaround the subscribers loop. When the armature of relay |04 breaks fromits right-hand Contact a circuit is available from negative battery |02,through resistance |08 and extending around the loop to positive battery|00. The resistance in this circuit is approximately twice as much aswhen the armature was on its righthand contact. The current around theloop for the travel time of thearmature from its right to its left-handcontact is, therefore, 30 milliamperes. When the armature of relay |04engages its left-hand contact, the batteries are opposed and the currentin the loop drops from 30 milliamperes to -0. At the end of the spacinginterval the loop current rises again to 30 milliamperes Where itremains during the travel time of the armature from its left-hand to itsrighthand contact. original condition, from 30 to 60 milliamperes.

Reference to Fig. 4 will disclose how this corrects the spacing bias.

Current in the loop during the interval until the armature of relay |04breaks from its righthand contact is indicated by the left-hand, top,horizontal line indicating 60 milliamperes. The armature breaks at r,which we may consider Zero time. This denes the start of the spacinginterval for relay |04. The current drops, still on the zero time lineto 30 milliamperes, indicated by line 1'-s, which is not quite lowenough tov-release the receiving relay in The current in the loopcontinues at 30 milliamperes during the travel time of relay |04armature from'itsright-hand, to its left-hand contact, in-

Then it rises instantly to the dicated by line sL-t. 'Ihen the'loopcurrent drops from 30 milliamperes to 0 amperes. It is not till thistime that the subscribers loop current passes through 29.9 milliamperes,indicated by the point marked Release where it is small enough to allowthe receiving relay in to release.Y This denes the start of the spacinginterval of the receiving relay. When the armature of relay |04 breaksfrom its left-hand contact at the beginning of its marking intervalindicated at v, the current in the loop rises instantly to 30 mils.,indicated by line '1J-w. This current is not great enough to operate thereceiving relay. The loop current remains at 30 mils. during the traveltime indicated by w:c. Then the loop current rises instantly to theoriginal condition indicated by x-y. During this rise the receivingrelay operates as the current reaches 30.1 milliamperes at a pointmarked Operate on line h-i. The spacing interval for relay |04 is thusmeasured by the time r-v. The spacing interval for the receiving relayis measured by the time '1L-au Since the travel times of the armature ofrelay |04 in each `direction are equal, the spacing'bias inherent inFig. 1 without branch |08-|02 is eliminated.

The effect of the spark protection apparatus upon bias will now beconsidered.

Fig. 3 is a time-current curve representing the pattern of the currentin the receiving relay at the subscribers station for themarking-to-spacing and spacing-to-marking transition of relays |04 andthe receiving rel-ay when the contact protection apparatus, resistances|06 and |01 and condensers and ||5 are employed without resistance |08and its connections.

The current flowing in the loop while the armature of relay |04 is inengagement with its right-hand Contact is, as indicated in Fig. 3, 60milliamperes. When said armature breaks from said contact, at point y',which defines the start of the spacing interval for relay |04, thecurrent does not drop instantly to 15 milliamperes, as in` the case forFig. 2, but dies more slowly, during the travel time, along the curvei-k, due to the discharge of the condenser. The receiving relay, insteadof releasing instantly, releases when-the current has decreased to 29.9milliamperes. This is indicated by the point marked Release on curvei-lc, which point defines the start of the spacing interval for thereceiving relay. At the end of the travel time indicated at 7c, thecurrent drops instantly to zero along line lc--L The loop currentremains at zero while the armature of relay |04 is in engagement withits left-hand contact, during the interval Z--n. At this point, which isthe end of the spacing interval of relay |04', the current rises, notinstantly, but more slowly, due to the action of the condenser, ltopoint 11, along the curve m-n. Then it rises instantly along the linen-p to 60 milliamperes. During this rise it passes through 30.1milliamperes at the point marked Operate which denotes the end of thespacing interval for the receiving relay.

It should be apparent, therefore, that the spacing interval for relay04, when the contact protection devices are used, and the inventionherein is not used, is equal to time im. The spacing interval for thereceiving relay is that between the points Release and Operate. Thesetwo time intervals are more nearly equal than for the condition per Fig.2. In other words, the contact protection devices alone, without theinvention herein, afford some improvementv for 'tlie"`spacingbiasinherent in Fig. 1, ove'rvcircuits in which neither the'protectiondevices nor the invention Iherein is applied. Furthermore, contactprotection networks affect bias in circuits per Fig. 1 not includingthis invention.

The loop current pattern per Fig.'5, which is obtained when theinvention herein and `contact protection devices, Ias indicated, areboth applied to a circuit per Fig. *1, will now be described.

The spacing interval for relay |04 starts at the point A, when thearmature breaks from its righthand contact. The loop current, due to theaction of the' condenser instead of dropping instantly on the break,declines along the curve A-B as the armature travels.' At B when thearmature engages its left-hand contact the current drops instantly tozero, passing through 29.9 milliamperes at the point on line B-C markedRelease which defines the start of the spacing interval of the receivingrelay. The current remains at zero while the armature and left-handcontact of relay |04 are in engagement. Then said armature breaks fromits contact at D. This denotes the end of the spacing interval for relay|04. The loop current rises to E instead of to 15 milliamperes alongcurve D-E. After the armature makes with its right-hand contact, at thepoint E, the loop current rises instantly to 60 milliamperes along lineE-F passing through 30.1 milliamperes at the point marked Operate whichmarks the end of the spacing interval for the receiving relay.

The spacing interval for relay |04, measured by time A-D is equal to thespacing interval for the receiving relay, measured by the horizontaldistance between the Release and Operate points for this relay as shownin Fig. 5. The spacing bias inherent in circuits per Fig. 1, when theinvention is not included in the circuit, is eliminated by means of theinvention and the bias is not affected by the contact'protectionnetworks.

This invention makes possible another improvement in the circuit perFig. 1 in addition to the elimination of spacing bias.

When the invention is not applied to Fig. 1, and the larmature of relay|04 is on its right-hand contact, the current flowing around thesubscribers loop is 60 milliamperes. The current through the bottomwinding of relay |09 and resistance ||3 is 30 milliamperes. All of thiscurrent totaling 90 milliamperes flows between the armature andright-hand contact of relay 04. When the armature of relay |04 is on itslefthand contact, there is no current in the loop and 30 milliamperesflow through the bottom winding of relay |09. This 30 milliamperes isthe total current flowing through the armature and left-hand contact ofrelay |04 when the two are engaged. Under these circumstances thetransient voltages and current lsurges developed as the armature makesand breaks with its two contacts vary. In designing contact protectionnetworks, it is necessary to take this into consideration.

When the invention herein is employed, and the armature of relay |04 isin engagement with its right-hand contact, the current flowing throughthe armature and right-hand contact is the same as heretofore,approximately 90 milliamperes. This is on the basis that resistance |03is practically negligible as compared with resistance |08 which is thecase. When the armature of relay |04 is on its left-hand contact,

again assuming resistance IJI negligible, the current through thearmature and left-'hand contact is approximately 90 milliamperes. 'Ihisfollows as the current through the bottom winding of relay |09 isunchanged and although vthere is no current in the loop as the batteriesat each end are opposed, a current equal in values to the loop currentfor the condition when the armature of relay |04 is on its right-handcontact now flows from positive battery through resistance IUI, theleft-hand contact and armature of relay |04 and resistance |08 tonegative battery |02. Thus approximately 90 milliamperes pass throughthe contact and armature of relay |04 for each condition. 'I'hetransient Voltage and current surges are the same for each condition.Identical contact protection networks may be used effectively for theprotection of each pair of contacts.

What is claimed is:

l. In a telegraph system, a telegraph relay comprising an armaturealternately engaging a first contact and a second contact, a iirstbattery and a second battery of voltage equal to the Voltage and ofpolarity opposite from that of said rst battery, connected each fromground to said rst and said second contacts respectively, a subscribersloop circuit of av rst resistance Value connected at one end to saidarmature and at the other end to said i'lrst battery, an artificial linecircuit of a resistance value equal to said first resistance Valueconnected at one end to ground and at the other end to said armature anda resistance element of a Value equal to the resistance value of saidloop, connected at one end to said second battery and at the other endto said armature.

2. In a telegraph system, a first telegraph station, a second telegraphstation, a sending and a receiving relay at said first station, areceiving relay at said second station, an armature on said sendingrelay, a telegraph loop extending from said armature through thewindings of said receiving relays, a balancingcircuit of resistanceequal to said loop resistance, extending from said armature through asecond winding on said receiving relay at said rst station to ground,and

a lumped resistance equal to the resistance of said loop circuit or saidbalancing circuit connected from the junction between said armature,said loop and said balancing circuit through battery to ground.

3. A balanced polar telegraph loop circuit comprising a loop and abalancing circuit connected in parallel to the fixed end of the armatureoi a telegraph sending relay, said circuit being characterized in that alumped resistance equal to the resistance of the loop is also connectedfrom said armature end to ground through one of the polar batteries.

4. A balanced polar telegraph loop circuit, a sending relay in saidcircuit having an armature, connected to o-ne end of said loop,operating between opposing contacts connected to equal batteries ofopposite polarities, the opposite end of said loop being connected toone of said batteries anda lumped resistance equal to the resistance ofsaid loop connected between said armature and the other of saidbatteries.'

5. In a balanced polar telegraph loop circuit, a telegraph sendingrelay, an armature on said relay operating alternately between opposingcontacts-connected to equal' batteries of opposite polarities,resistance and battery means in said circuit for transmitting fullcurrent around said loop when said armature is in engagement with one ofsaid contacts, battery means for transmitting Zero current around saidloop when said armature is in engagement with the other of saidcontacts, and battery and resistance means connected to said circuit fortransmitting half current around said loop when said armature istraveling between contacts.

6. In a balanced polar telegraph loop circuit, a telegraph sendingrelay, an armature on said relay, a iirst and a second contact also onsaid relay, a first battery of a first polarity connected to said rstcontact, a second battery of electromotivev force equal to and ofpolarity opposite from said first battery connected to said secondcontact, means for transmitting current of a iirst value around saidloop when said armature is in engagement with said rst contact, meansfor transmitting current smaller in value than said first value aroundsaid loop when said armature is in engagement with said second contactand means for transmitting currents through said armature and saidcontacts equal in Value each to each when said armature is in engagementwith said contacts.

7. In a balanced polar telegraph loop circuit, a transmitting relay at afirst station, an armature on said relay, a marking and a spacingcontact also on said relay, a receiving relay at a second station, meansfor delaying the release of said receiving relay until said armature hastraveled from its marking to its spacing contact,

and means for delaying the operation of said receiving relay until lsaidarmature has returned to its marking contact.

8. In a balanced polar telegraph loop circuit, a polar transmittingrelay at a rst station, an armature on said relay operating between; amarking and a spacing contact also on said relay, a receiving relay in asecond station, both of said relays connected to said circuit, meansalso connected to said circuit for equalizing the current flowing aroundsaid loop through said receiving relay during the travel of saidarmature between said contacts in each direction, means connected tosaid circuit for maintaining said loop current above the release currentvalue of said receiving relay for said armature travel in one directionand below the operate current value of said receiving relay for saidarmature travel in the opposite direction.

HARRY NYQUIST.

